Identification of Transcription Factors Responsible for a Transforming Growth Factor-β-Driven Hypertrophy-like Phenotype in Human Osteoarthritic Chondrocytes

Abstract

During osteoarthritis (OA), hypertrophy-like chondrocytes contribute to the disease process. TGF-β’s signaling pathways can contribute to a hypertrophy(-like) phenotype in chondrocytes, especially at high doses of TGF-β. In this study, we examine which transcription factors (TFs) are activated and involved in TGF-β-dependent induction of a hypertrophy-like phenotype in human OA chondrocytes. We found that TGF-β, at levels found in synovial fluid in OA patients, induces hypertrophic differentiation, as characterized by increased expression of RUNX2, COL10A1, COL1A1, VEGFA and IHH. Using luciferase-based TF activity assays, we observed that the expression of these hypertrophy genes positively correlated to SMAD3:4, STAT3 and AP1 activity. Blocking these TFs using specific inhibitors for ALK-5-induced SMAD signaling (5 µM SB-505124), JAK-STAT signaling (1 µM Tofacitinib) and JNK signaling (10 µM SP-600125) led to the striking observation that only SB-505124 repressed the expression of hypertrophy factors in TGF-β-stimulated chondrocytes. Therefore, we conclude that ALK5 kinase activity is essential for TGF-β-induced expression of crucial hypertrophy factors in chondrocytes.

Cbfβ Is a Novel Modulator against Osteoarthritis by Maintaining Articular Cartilage Homeostasis through TGF-β Signaling

“…The tight control of TGF-β signaling plays an essential role in articular cartilage homeostasis [ 10 ]. The injection of TGF-β into the knee joint increases proteoglycan, whereas the injection of recombinant soluble TGF-β type II receptor, an endogenous inhibitor, markedly worsens OA phenotypes [ 11 , 12 ].…”

Cbfβ Is a Novel Modulator Against Osteoarthritis by Maintaining Articular Cartilage Homeostasis Through TGF-Ꞵ Signaling

“…Physiological maintenance of articular cartilage requires tight control of the TGF-ꞵ signaling pathway [10]. Our study demonstrates the critical role of Cbfβ and Runx1 as a mediator of TGF-ꞵ signaling (Fig.…”

“…Tight control of TGF-ꞵ signaling plays an essential role in articular cartilage homeostasis [10]. Injection of TGF-ꞵ into the knee joint increases proteoglycan, whereas injection of recombinant soluble TGF-ꞵ type II receptor, an endogenous inhibitor, markedly worsens OA phenotypes [11,12].…”

The Critical Role of Hypoxia in the Re-Differentiation of Human Articular Chondrocytes

“…However, COL10A1 expression was significantly lowered in spheroids under hypoxic conditions than in normoxia after 14 days of culture with a chondrogenic medium ( Figure 5 b). It has been demonstrated in recent studies that TGF-β, found in the chondrogenic medium, can drive hypertrophic differentiation in chondrocytes while also inducing its leading role as a transforming growth factor in cartilage differentiation [ 41 , 42 , 43 , 44 ].…”